Multicore chips have more than one CPU core; multiple-processor computers
have more than one CPU chip. Both have been introduced by manufacturers to
speed up tasks by splitting threads or processes among different
processors so that they can be performed in parallel.

In addition, Mathematica's notebook front end is a separate process
from its computational kernel, allowing them to run on separate cores or CPUs.
This gives a responsive interface even when the kernel core is under full
load.